1. Technical Field
The present invention relates in general to improving the stealth capability of an optical instrument and, in particular, to an improved system, method, and apparatus for improving the stealth capability of an optical instrument.
2. Description of the Related Art
Optical devices often contain one or more lenses or other reflective surfaces. For example, optical devices for ranging, guidance, communication or information gathering, such as binoculars, telescopes, periscopes, rifle scopes and the like, all contain one or more lenses that can reflect incident light. Laser beam detection devices have found increased use in locating and/or ranging functions, particularly in military applications, and rely on analysis of reflected beams to detect and/or determine the position of an apparatus that contains a reflective surface, for example such optical devices as mentioned above. For example, a scanning laser may be projected across a combat area to determine an enemy's location. Reflected laser beams from a reflective surface of an optical device can be analyzed to determine the presence and location of the source of reflection.
Such scanning as well as targeting, ranging, designating and offensive lasers are capable of causing eye injury and, as a safety measure, soldiers and others who might be exposed to such beams frequently include dielectric or other filters in optical devices to prevent transmissions of harmful light to the eye. For example, laser protective filters have been incorporated into optical devices used in military settings, such as armored vehicle sights, binoculars and the like. The protective filters are often positioned behind one or more optical elements, e.g., behind one or more transparent or translucent lenses. Alternatively, the protective filters may be positioned in front of an optical device, such as in front of the outermost lens element of the device. In particular, to retrofit optical devices such as a scope to include a laser protective filter, often the only cost effective or practical place to put the filter is in front of the device.
While such laser protective filters can effectively block transmission of harmful electromagnetic radiation, the filters are typically highly reflective and thus can produce reflections of incident light, such as light of the dome of the sky, the sun or a scanning laser beam that can be readily detected by a viewer. As used herein, the term viewer refers to both a person and/or an apparatus for detecting such items. Moreover, a protective filter positioned in the front of an optical device, such as in the case of a retrofitted device, is particularly prone to produce reflections that can be readily discerned by a viewer.
In military situations, reflections from certain sensors that are part of optical systems also can be a problem. These sensors, such as charged coupled devices in video cameras, are typically reflective surfaces, and thus can generate retro-reflections back through the optical system, much in the way that at night, reflections of light from a car's headlights can be seen from a cat's retina. Such retro-reflections from a sensor element can be a serious problem, particularly in military situations. Systems are employed that scan a battlefield with a laser looking for retro-reflections such as from sensor elements located at the focal plane or other reflective surfaces within an optical system such as thermal sights and armor vehicle sights. The laser scanning systems use these retro-reflections from such optical devices to locate, identify and/or target the optical devices for offensive fire.
There are other instances where it is also very undesirable to have light reflected from an observing instrument returned to an object or scene being imaged or viewed. For example, in some chemistry experiments involving chemo-luminescence, a chemical reaction results in the production of light, and the quantity or time-rate of production of this light may provide an indication of the rate of the chemical reaction.
Another example is provided by particle physics in which the light produced by particle interactions with one another or with an indicator medium is of importance in detecting the fact of or the nature of such particle interactions, or their path in a magnetic or electric field, for example. In such cases, and others, the reflection of light from an optical observation instrument back into the scene being viewed or back to an object being viewed can be very detrimental. Thus, an improved system, method, and apparatus for improving the stealth capability of an optical instrument would be desirable.